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Planning on making my own semi-auto

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Planning on making my own semi-auto

Unread postAuthor: noname » Thu Sep 27, 2007 11:44 pm

I've wanted to make a portable, semi auto (or 3-5 shot burst) airsoft gun for quite some time, but never really got around to it. JSR, you're the one who gave me the idea to try again, and I'll probably be making a close copy of your first 6mm semi. I've also had lots of fun blasting out over 100 BBs per second, but it gets kind of old after so long. Semi auto is actually harder to make than full auto, and burst fire is probably harder than either. I'll just stick to semi for now, and maybe modify it later.
The gun will have three different pressure tanks. One will be a propane tank, as the pressure source. It will be hooked up to a 1" Sch 80 x 6-8" long expansion chamber. Then there will be a pressure regulator to a small, 1/2" x 3-4" chamber, the firing chamber. The firing valve will be a sprinkler valve, piloted by a blowgun. I'm not really going for power, because I'd like to use this in small airsoft "wars" (more like little skirmishes).
Should be fun once I finish it, but it won't be done for a couple weeks, most likely.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 28, 2007 1:32 am

I'm not really going for power, because I'd like to use this in small airsoft "wars" (more like little skirmishes).


If so, why not just use the blowgun as the firing valve? In my design a blowgun trigger gave me over 400 fps with 0.25g BB, pretty hefty power for airsoft (I haven't tried with 0.12g but I imagine the velocity increase would give a flatter trajectory at short range and a nasty sting to your targets :D) plus unlike a sprinkler valve, it reseals the instant you let go of the trigger.
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Unread postAuthor: noname » Fri Sep 28, 2007 6:56 pm

JSR wrote:unlike a sprinkler valve, it reseals the instant you let go of the trigger.


A sprinkler does reseal if you let go of the trigger, provided it's modified with a blowgun and it's non-electrical. I would definitely use a blowgun over a sprinkler anyway, but a blowgun doesn't have the configuration I need. I want it to have a trigger, but the valve has to be inline. I could make my own inline diaphragm valve but those get fiddly when you get small and it has to reseal automatically.
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Unread postAuthor: windshrike » Fri Sep 28, 2007 7:02 pm

Nope, sprinklers don't auto-reseal. You need a very small flow refilling a sprinkler for it to reseal quickly, and flow that small takes time to refill. I have put .12g bbs through both sides of a can with a leaky blowgun alone at 110-120 psi(told you it leaked). If you drilled out the valve in a blowgun to increase flow, power would dramatically increase.
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Unread postAuthor: MrCrowley » Fri Sep 28, 2007 7:04 pm

Every S Valve I have used, re-seals, because it dumps only about 99% of the air, the rest seals the valve, for me anyway, that's how I can use mine semi-auto.
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Unread postAuthor: noname » Fri Sep 28, 2007 7:04 pm

Every sprinkler I've used pneumatically for the past 3 years has automatically resealed. Is that a good enough answer?
And I'm not going to use a blowgun, like I've said already.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 28, 2007 10:44 pm

I that case, let me swing to the other extreme - following on from what I'm doing here, I think my next step will be to adapt my blow-forward bolt to attach to the nailgun.

It does take out the homebuilt aspect somewhat but a small finishing nailgun is a semi-automatic piston valve cannon that can be obtained for less than a QEV, I don't know why more people haven't been playing with them. I remember this project on spudtech by nxi but nothing else.
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Unread postAuthor: noname » Tue Oct 02, 2007 8:56 pm

The main chamber is done, but I'm dumping it, the regulator, and the sprinkler valve. Instead, I'm just going to hook up propane (possibly regulated) to the main valve, a blowgun.
I have all the parts for the blow forward bolt. I have the tube that contains everything done (1" PVC), with an epoxy plug in the back. I have a round plug of epoxy for the bolt. I have a perfect spring. I have the magazine set up. I have the barrel, some 1/4" brakeline for the bolt, some 1/4" aluminum rod, and I'll probably work on it this weekend.

I'm scared. Last time I tried this I ruined the whole project because I can never center everything perfectly and that's a must for this project.
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Unread postAuthor: Wombat » Sat Oct 13, 2007 9:42 pm

I'm also planning on building a semi-auto valve similar to the one created by JSM. In his nail-gun+6mm semi thread, I think he talked about making the valve smaller. Thats what I intend to do. I will make the chamber out of brass tubing from Ace Hardware, and this website - www.mcmaster.com Brass is sold in a wide variety of sizes, and the good part is that they can fit inside one another nearly perfectly. Instead of trying to cast the parts completely out of epoxy, I'll make them out of pieces of brass glued together.
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Unread postAuthor: VH_man » Sat Oct 13, 2007 10:28 pm

wombat, you think like me.... lol. in fact thats what im currently doing, exept MARBLE CALIBRE!!!!!!!

my only problem at the moment is the fact i tried using a spring-fed magazine. and i lack a consistent source of air. im saving up for a CO2 setup. and then DAMNNN those marbles will fly......
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